1. Field of the Invention
The invention relates to a common rail fuel injection system for internal combustion engines, having a pressure regulating valve for regulating the pressure in a common rail, having a pistonlike valve member guided axially displaceably in a bore, which valve member acts in the closing direction on a closing element and presses it against a valve seat, and the valve member forms an armature of an electromagnet that can be supplied with electric current.
2. Description of the Prior Art
Many versions of pressure regulating valves of the type with which this invention is concerned are known for regulating the pressure in a common rail, with which it communicates via an inlet. The pressure regulating valve has a pistonlike valve member, which is guided axially displaceably in a bore and can move counter to a force which is exerted on the valve member preferably by the current in the electromagnet. The force acts in the closing direction, so that the valve member is pressed against a closing element of the pressure regulating valve and against a valve seat. The valve member forms an armature of an electromagnet, which can be supplied with current to control the force.
By means of the supply of current, the closing element is pressed via the valve member against the valve seat with a certain force, whereupon as a result of the pressure acting on it the closing element is lifted from the valve seat in the common rail, if the force generated by the pressure exceeds the closing force that is exerted on the closing element via the valve member. If so, fuel flows out of the common rail into a relief chamber via the opened pressure regulating valve.
If a higher pressure is set in the common rail, the current in the electromagnet is increased, thus increasing the closing force, and accordingly only at a higher pressure in the common rail does the closing element lift from the valve seat and allow fuel to flow out of the common rail into the relief chamber.
In addition, the valve is often provided with a mechanical spring, which in its state of repose, that is, while the engine is stopped, assures that the valve is closed and fuel cannot get into the relief chamber. The mechanical spring force of this spring, however, can already easily be overcome by a slight fuel pressure. It is then impossible for a sufficiently high pressure to be built up in the common rail. The requisite minimum pressure in the common rail is assured only by the action of the electromagnetically generated closing force.
If some malfunction in supplying current to the electromagnet occurs, for instance from loosening of the plug involved, causing a failure of the electromagnetic closing force, then fuel at low pressure can get into the relief chamber and make an injection possible. The vehicle can then no longer be driven.